This invention relates to a telecommunications switching system, and more particularly to automatic fault recovery in such a system.
U.S. Pat. No. 4,146,749 to Pepping et al. and U.S. Pat. application Ser. No. 842,091 of Pitroda et al. (now Patent No. 4,256,926) describe a telecommunications switching system controlled by a complex of multiple microprocessors. The system provides a number of standby or spare portions which can be switched into operation in the event of a malfunction. The present application is generally concerned with the automatic switching of such spares. In particular, the present application is directly concerned with the switching between duplicate processors, buses, memory modules, etc. of the control complex as disclosed in the Pitroda et al. application, rather than the spare network block of the Pepping et al. patent.
The general object of the present invention is to provide a system which can isolate the source of a detected error, in some cases correct the error and in other cases reconfigure the operation of the system appropriately. There are several major factors which influence the solutions conceived to attain this objective. For one thing, the control complex in which all of this is to be carried out, is made up of multiple processors, rather than a single multiprogrammed processor. Secondly, it is difficult to analyze soft faults, arising from noisy components, as opposed to hard faults due to a totally failed component. Thirdly, it is highly advantageous to minimize the disruption of the large number of communications which may be connected through the switching system. The importance of these factors in the present invention will become apparent upon a consideration of the detailed disclosure below. Because these factors are present in other kinds of systems, the teachings of the present invention can have applicability beyond the switching system described in the Pepping et al. patent and the Pitroda et al. application.